Brownfield brings the best from piling specialist

// the building envelope

HA Magazine hears from John Patch of Roger Bullivant Limited about the boom in brownfield and basement projects which is keeping his company busy in our urban areas.

The opulent ambitions of Premiership footballers and foreign oligarchs, as well as some badly botched contracts where homes have actually collapsed into the excavations, have resulted in so called “super-basements” getting considerable coverage in the newspapers over recent years. These mainly being dug out from beneath already large properties in the districts of Kensington and Chelsea. 

There are, however, many much larger sub-structures being created in towns and cities across the country, as developers call on the services of piling specialists like Roger Bullivant to provide the required retaining structures. Given the demand for new commercial as well as residential property to accommodate a growing population and a recovering economy, it seems likely this sort of work will be on the increase.

Roger Bullivant’s John Patch recounts: “There is a definite increase in the number of infill sites being built on – ones which previously wouldn’t have been reused or that are subject to demolition and change of use. In a lot of cases it is due to the changes in planning regulations, and we are seeing, for instance, former industrial buildings being turned to residential use. It is also not unusual to see an existing building being extended or to have new accommodation wrapped around it."

“What these urban sites require, though, is underground car parking; with the consent requiring sufficient spaces to be created not just for the residents of the flats, but also for visitors."

“These therefore are often double or even triple level structures, and the normal solution for their perimeter retaining walls is to sink bored, contiguous piles. Proximity to neighbouring properties normally prevents use of ground anchors to counter the overturning moment, so the basement and ground floor constructions have to be designed to prop the retaining walls; otherwise you would need to sink the piles to a depth of approximately 18 metres for a six metres basement height.”

While I imagined that the retaining walls would be constructed using 600 or 750mm and even 900mm diameter piles to reduce the total number required, John explained that in fact, heavily reinforced 450 mm diameter piles are often preferred, simply to save space. This is because around a large basement, the half metre recovered from the width of the retaining wall can amount to several dozen extra bays.

Technical details on bored piling

In addition to this full scale redevelopment of previously used sites, Roger Bullivant is also regularly requested to carry out underpinning or stabilization operations: normally employing its mini-piling rigs which can be set up within relatively restricted spaces.

John Patch concludes: “Clearly there is a massive amount of brown field site available for development across the UK, including in former industrial land, and we in the industry are very pleased to play our part in bringing these areas back into use. For economic, social and environmental reasons these sites should be reused, but they require both thorough investigation for issues such asbestos and other forms of contamination, as well as the structural solutions for remediating them.”

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